1. Field of the Invention
The present invention relates to a narrow band interference detector, and more particularly, to a narrow band interference detector for a receiver of a communication system to detect narrow band interference signals in time domain.
2. Description of the Prior Art
Global positioning system (GPS) is an accurate navigation system and generally used in civilian or military applications. The performance of GPS receiver is usually degraded by intentional or unintentional narrow band interference signals in input signals. The narrow band interference signals may reduce signal to noise ratio (SNR) of a receiver of a GPS system, cause satellite determination error, increase Time to First Fix (TTFF), and lower navigation accuracy, etc. Therefore, the receiver is generally required to detect and cancel the narrow band interference signals.
A conventional narrow band interference detector of the GPS receiver generally applies fast Fourier transform (FFT) to detect frequencies of the narrow band interference signals in a frequency domain (FD), and thus a conventional narrow band interference canceller of the GPS receiver can utilize time domain (TD) notch filters or FD notch filters to cancel the narrow band interference signals from the input signal.
However, since the conventional narrow band interference detector applies FFT to detect the frequencies of the narrow band interference signals in the FD, when a narrow band interference signal type of an narrow band interference signal is an unmodulated signal (e.g. only one pure tone), the conventional narrow band interference detector needs to apply excess FFT numbers (i.e. excess cost) for accuracy, to avoid estimate error of the frequency of the unmodulated signal resulted from limited FFT numbers.